Nitrogen source effects on Al toxicity in nonmycorrhizal and mycorrhizal pitch pine (Pinus rigida) seedlings. I. Growth and nutrition

Abstract

Previous studies indicated that the association of Pisolithus tinctorius with pitch pine (Pinus rigida) seedling roots prevented Al toxicity from developing when seedlings were exposed to 200 μM Al in sand culture. The ectomycorrhizal fungus reduced seedling Al uptake and maintained P nutrition when seedlings were cultured on one-quarter strength Johnson's solution containing 3.5 and 0.5 mM [Formula: see text] and [Formula: see text], respectively. To broaden the scope of these findings, nonmycorrhizal and mycorrhizal seedlings were grown on one-quarter strength Johnson's solution modified to contain [Formula: see text], NH4NO3, or [Formula: see text]. Seedlings were exposed to 0 or 200 μM Al for 6 weeks. Reductions in seedling height growth rate and final shoot weight in response to Al occurred in nonmycorrhizal seedlings grown with [Formula: see text]. Root weights were consistently reduced by Al under all N-source combinations. Increasing proportions of [Formula: see text], in the nutrient solution increased cation accumulation in roots and shoots and depressed tissue anion concentrations. The coprecipitation of Al and Pi in roots of Al-treated seedlings further limited P availability in this treatment. Mycorrhizal infection maintained growth and foliar P levels under Al exposure, suggesting that Al-induced P limitation was a critical factor in nonmycorrhizal seedlings grown on primarily [Formula: see text]-based nutrient solutions. Key words: Pinus rigida, ectomycorrhizal, aluminium toxicity, nitrogen source.